The shield tunneling method plays an important role in civil engineering works. Providing segments with flexibility is essential to avoid damage to shield segments per se and to ensure safety in weak ground in the event of uneven settlement or earthquake. Various investigations have been carried out in this area thus far. In general, such flexible segments are installed in the shell of a shield machine and are set by means of thrust application together with general segments, then load-bearing members and sealing members are installed on the inner surfaces of these flexible and general segments for application of a secondary concrete coating on the inner surfaces of said general segments.
An application example of such a flexible segment is shown in FIG. 10. The primary application member 50, consisting of frame members 21 and 21, which also serve as secondary coating, and thrust-receiving member 22, is installed with an erector, etc., in the row of general segments 20, which are standard members, in the shell 51 of a shield machine, and thrust excavation application is then performed in which thrust from the shield machine acts on the general segments 20 and the primary application member 50.
On completion of thrust transmission with the thrust application performed in the above manner, said thrust-receiving member 22 is removed, a flexible, secondary watertight member 22 is installed as shown in FIG. 11, and at the same time, the cover cloth 25, load-bearing member 26, and load-bearing sleeve 27 are also installed, and secondary coating 23 is applied to the anchor 28 as shown in FIG. 12.
With conventional methods such as that described above, the structure and handling are complicated, requiring a substantial number of man-hours in the field. To be more precise, in the states shown in FIGS. 10 and 12, the frame member 21 is the only member that remains the same between general segments 20, and the other members and the structural relationships are totally different. With such a configuration, each segment or member is removed sequentially and another segment or member is installed on the entire periphery of the excavated hole formed with a circular cross-sectional shape. This inevitably requires a substantial number of man-hours.
Furthermore, since frame members which are considerably thicker than general segments 20 are used in the primary application, their handling during assembly is extremely different from that of standard, general segments, making the work complicated. The main members such as the thrust-receiving member, which are installed and connected together during thrust application as shown in FIGS. 10 and 11, are removed and completely separated and then new, separate members are installed. The watertight linkage and sealing which is established during thrust application is lost through the handling of the new members, and new linkage and sealing is established when new members are installed. Therefore, appropriate watertightness and stress distribution are difficult to obtain.